<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>表单验证</title>
    <style>
      form {
        width: 400px;
        border: 10px solid pink;
        padding: 20px;
      }

      label {
        display: block;
        height: 80px;
        position: relative;
      }

      input {
        height: 30px;
        font-size: 24px;
        padding-left: 20px;
      }

      label > span {
        position: absolute;
        left: 0;
        top: 35px;
        font-size: 20px;
        color: red;
        display: none;
      }
    </style>
  </head>
  <body>
    <form>
      <label>
        用户名: <input class="username" type="text" />
        <!-- 数字字母开头6～12位 忽略大小写 -->
        <span>请按照规则填写用户名</span>
      </label>
      <label>
        密码: <input class="password" type="text" />
        <!-- 数字字母下划线 6～12位 -->
        <span>请按照规则填写密码</span>
      </label>
      <label>
        手机号: <input class="phone" type="text" />
        <!-- 11位数字即可 -->
        <span>请按照规则填写手机号</span>
      </label>
      <label>
        邮箱: <input class="email" type="text" />
        <!-- 6～12位 开头为数字大小写字母 中间为数字字母下划线均可-->
        <!-- @ 只接收qq 163 sina -->
        <!-- com或者cn -->
        <span>请按照规则填写邮箱</span>
      </label>
      <input type="button" value="完善资料" />
    </form>
    <script>
      var username = document.querySelector('.username')
      var password = document.querySelector('.password')
      var phone = document.querySelector('.phone')
      var email = document.querySelector('.email')

      username.addEventListener('input',function(){
        var reg = /^[0-9a-zA-Z]\w{5,11}$/i;
        var err = document.querySelector(".username~span");
        err.style.display = reg.test(username.value) ? "none":"block";
      })

      password.addEventListener('input',function(){
        var reg = /^\w{6,12}$/;
        var err = document.querySelector(".password~span");
        err.style.display = reg.test(password.value) ? "none":"block";
      })

      phone.addEventListener('input',function(){
        var reg = /^\d{11}$/;
        var err = document.querySelector(".phone~span");
        err.style.display = reg.test(phone.value) ? "none":"block";
      })

      email.addEventListener('input',function(){
        var reg = /^[0-9a-zA-Z]\w{4,10}@(qq|163|sina)\.(com|cn)$/;
        var err = document.querySelector(".email~span");
        err.style.display = reg.test(email.value) ? "none":"block";
      })

    </script>
  </body>
</html>
